Modified Denavit-Hartenberg parameters

Work in progress, use one the other libraries below (Inspiration)

Build kinematic chains using the modified Denavit-Hartenberg paramters

• d: offset along previous z to the common normal
• theta: angle about previous z, from old x to new x
• a: length of the common normal, assuming a revolute joint, this is the radius about previous z.
• alpha: angle about common normal, from old z axis to new z axis

You should probably use one of these, they inspired me to write a simpler module for my needs:

• pybotics
• pytransform3d, some matplotlib 3d examples
• robopy, has some good matplotlib 3d examples, but seems rather brittle and difficult to work with
• tinyik, uses open3d to visualize the mechanism

import numpy as np
from mdh.kinematic_chain import KinematicChain
from mdh import UnReachable # exception

# make it print better
np.set_printoptions(suppress=True)

# modified DH parameters: alpha a theta d
# types: revolute=1, prismatic=2 (not implemented yet)
dh = [
    {'alpha': 0,  'a': 0, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': pi/2, 'a': 52, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 89, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 90, 'theta': 0, 'd': 0, 'type': 1},
    {'alpha': 0, 'a': 95, 'theta': 0, 'd': 0, 'type': 1}
]

kc = KinematicChain.from_parameters(dh)

# forward kinematics
angles = np.deg2rad([-45.00, 77.41, -98.15, -69.27, 0])
t = kc.forward(angles)
print(f">> {t}")

# inverse kinematics
pt = [110,0,-70]
deg = kc.inverse(pt)
rad = np.rad2deg(deg)
print(f">> {rad}")

Copyright (c) 2019 Kevin J. Walchko

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